Water Flow, Soil Temperature, and Carbon Dioxide Concentrations in a Burning Coal Refuse Pile

Many coal refuse piles in the Appalachian region present combustion zones as well as rapid groundwater flow and discharge of acidic waters. At the Misco Pile, in Perry County, Ohio, pyritic refuse from an underground coal mine was dumped as valley fill from 1945 to1954. Prior to recent remediation of the refuse pile, damming of a creek by the refuse pile produced a 0.02-km2 pond that collected water from the surrounding watershed. The refuse pile had two plateaus and two slopes in stair-step fashion. Pond water flowed through the pile, discharging to an adjacent stream with a pH 2.6 from the pile toe. Investigation of the water budget, soil temperatures at 0.9 m, and concentrations of CO2 at selected points was done to understand the groundwater flow processes, transport of pyrite oxidation reaction products, and thermal processes within the pile. The water budget of the pile and its watershed was evaluated using meteorological information, estimated evapotranspiration and infiltration to the refuse pile. The outflow from the refuse pile accounted only for about 60% of the water entering the pile, suggesting water loss to the abandoned flooded mine beneath the valley floor via fractures in an intervening sandstone unit. Based on a thermal survey over the refuse pile surface, burning was confined to erosion gullies on the lower plateau. CO2 concentrations and temperatures suggested that convection was drawing air into the pile from the lower slope and venting it from the lower plateau. Convection was driven by exothermic pyrite oxidation and coal combustion, perpetuating the cycle. Erosion increased the surface area of refuse exposed to the atmosphere, promoting combustion along gullies. Implications of the mechanisms controlling combustion and acid mine drainage are that control of the impoundment drainage and refuse capping to limit erosion and air circulation were key remediation objectives.